Method of treating solid surfaces



Feb. 18, 1969 w. MAASBERG E'f AL 3,427,763

METHOD OF TREATING SOLID SURFACES Filed July 18, 1966 Sheet WOLFGANG MAASBERG WILLI HEINRICH INVENTOR.

1969 w. MAASBERG ETAL 3,427,763

METHOD OF TREATING SOLID SURFACES Filed July 18, 1966 Sheet 2 of 4 WOLFGANG MAASBERG WILLI HEINRICH INVENTOR.

Attorney 18, 1959 w. MAASBERG ET AL 3, 6

METHOD OF TREATING SOLID SURFA ES Sheet Filed July 18, 1 966 FIG.6

R E w w W w A M m Alv g m MRm 1A am M NE AH ml u OI ww Feb. 18, 1969 w, MAASBERG ET AL 3,42

METHOD OF TREATING SOLID SURFACES Sheet Filed July 18, 1966 WOLFGANG MAASBERG WILLI HEINRICH INVENTOR.

United States Patent 4 Claims ABSTRACT OF THE DISCLOSURE A method of treating a surface in which a recirculated mixture of sand, quartz particles, corundum or fly ash with a particle size of 0.01 to 3 mm. (preferably 0.1 to 1 mm.) is directed against the surface in a water jet at a pressure of 100 to 900 atmospheres, the jet having a diameter of 2 to 3 mm.

Our present invention relates to a method of treatingmetallic, stone, synthetic resin or other solid surfaces for the removal of adherent deposits (e.g. scale and cinders), for the polishing, erosion, roughening, or workhardening thereof, and for the cuting or drilling of the solid body through such surfaces and the like.

The surface treatment of solid bodies for descaling, roughening, polishing or otherwise modifying the characteristics of the exposed faces of a solid body and the cutting of stone and the like has been carried out heretofore with tools and devices some of which utilize the technique of sand or shot blasting. Thus it has been proposed heretofore to descale the exposed surfaces of a. metallic body (e.g. cast-metal articles) to remove oxide scale, adherent particles or scab, mold sand, or oxide layers by subjecting the metallic surfaces to a high-velocity jet of gas (e.g. air) entrained sand or shot particles. For the most part, relatively small-diameter particles must be used in order not to pit adversely the surface treated and it has been found that such treatments are not wholly satisfactory because the sand or other treating particles frequently remain or lodge in pores, crevices, depressions and roughenings in the surface end and are held therein under great force because of the kinetic energy of the original impact. Removal of such particles, subsequently, is difficult and time-consuming and the presence of such particles frequently prevents further surface treatment or renders the body unusable. Because of these drawbacks, it has been proposed to use chemical methods for the descaling of wire or the like butthese methods tend to corrode the metallic body, require com plex apparatus and cannot be carried out with bodies of varying configurations and size without substantial modification.

Furthermore, the use of sand-blasting methods to treat metallic and nonmetallic surfaces (e.g. for polishing, grinding, roughening) has the further disadvantage that the spray of sand does not permit a sharp and well-defined boundary between the treated and nontreated surfaces, permits particles to lodge in pores of the body, dissipates a large portion of the kinetic energy of the particles in elastic impact, and is difficult to use for forming relatively narrow recesses, cuts or openings in the surface of the body.

It is,, therefore, the principal object of the present invention to provide an improved method of treating the surfaces of a solid body which avoids the aforementioned disadvantages and has relatively widespread application with respect to the type of surface treatment, the nature of the solid body, the confines of the treatment and the depth of penetration thereof.

A more specific object of this invention is to provide a system of great versatility which can be used for the descaling of metal bodies, for the surface treatment of stone bodies, for the drilling or cutting of solids of various description and for polishing as well as erosion of a surface.

Another specific object of our invention is to provide an improved method of descaling metal surfaces and, more particularly, the descaling of cast-iron pipes, drawn metallic wire, weld seams, and the like.

A further specific object of this invention is to provide an improved method of cutting (e.g. drilling or severing) metallic bodies in a rapid and efficient manner without material deterioration of a tool.

Yet a further specific object of our invention is to provide a method of cutting or drilling natural and synthetic stone surfaces and especially concrete which can be carried out relatively quickly, with a minimum of mechanical stress to the body.

Another specific object of our invention is to provide an improved method of and apparatus for the polishing, grinding or erosion of a solid surface without requiring the use of massive devices and suitable for use at different locations.

We have surprisingly discovered that many of the disadvantages of prior-art treatment of solid surfaces, the' drilling and boring of synthetic or natural stone, and the descaling of metal bodies or the like can be obviated by comparison with sand or shotblasting techniques when the surface treatment is carried out by means of a high-pressure high-velocity liquid stream directed at the surface and entraining therewith a granular or particulate material in such manner that the liquid medium constitutes a viscous matrix (by comparison with gaseous entrainment of solid particles) of limited elasticity and rebounding character. It appears that the solid particles entrained by the liquid are able to transfer their kinetic energy to the workpiece and have, in turn, a greater useful kinetic energy by virtue of the fact that the rebound from and impact upon the surface to be treated is restricted by the viscous medium in which they are entrained. Moreover, the liquid acts as a lubricant, preventing or restricting erosion of the nozzle or jet from which the particles are dispensed. Still another advantage of this technique is the fact that the liquid prevents scattering of the particles and thus permits a well-defined machining or treatment of the surface. Additionally, it may be observed that the liquid medium prevents the particles from being dispersed in the atmosphere and thus the treatment process of the present invention can be carried out without the need for dust-collecting apparatus and with fewer precautions with respect to the health and well-being of the operators of the system. In general, we have discovered that the present system requires liquid pressures of at least atmospheres and can be carried out effectively with liquid pressures up to about 900 atmospheres at the nozzle. The particulate material can be any abrasive substance including ordinary sand, quartz sands, corundum, slag sands, flue ash and the like, the hardness or abrasive character being determined by the material to be treated. It will be understood, however, that the liquid pressure at the nozzle, the spray-cone angle or spread of the jet of liquid-entrained solid particles and the volume per unit time of the abrasive medium in its viscous matrix will depend upon the particular surface treatment under consideration. The same holds true for the particle size of the treatment agent. For the most part it can be stated that the particles should have a particle size ranging between 0.01 and about 3 mm.

According to a more specific feature of this invention, the process is used to cut or drill metallic workpieces without the need for rapidly wearing saws, stones, drills and the like expensive machining tools and without the aid of cutting torches and the like. The present invention is thus applicable for workpieces with high melting points and high hardness, such metals being difficult to process with conventional cutting-torch arrangements and cutting tools.

It appears that the use of a high-pressure water or other liquid streams with very high velocity to entrain abrasive particles against a metallic surface of even the hardest composition affords a rapid cutting and drilling of the metallic body because of the fact that the viscous matrix causes the particles to move along the metallic surface in the manner of the abrasive particles of a grinding wheel or the like, i.e. in an erosive sliding manner. By contrast, sandblasting and shot-peening systems effect a substantially complete transfer of kinetic energy from an impacting particle to the metallic surface and results in the formation permanently or temporarily of a recess as this particle is urged with its considerable energy into the surface. Considerable surface roughening and pitting results. When, however, the particles are entrained in a liquid stream of the character described, the particles appear to be at least in part diverted along with the liquid film flowing over the surface, i.e. parallel thereto, so that the sharp edges and surfaces of the abrasive particle erode the surface without forming depressions and without materially rebounding from the surface. It will be understood further that this method is particularly suitable for metallic surfaces having recesses prior to the treatment inasmuch as the tendency for particles to become driven into these recesses in a nonremovable manner is markedly reduced. The cutting action is thus similar to that resulting from the application of a grinding stone or saw against the metal surface although the absence of any wearable tool renders the present method a marked improvement over conventional methods of cutting and drilling. Moreover, the problem of heat-transfer from a metal body subjected to cutting and drilling by conventional methods is completely obviated because the viscous liquid entrained the abrasive particles constantly passes in heat-exchanging relationship, with the surface of the body and temperature increases are precluded. The width of the high-pressure liquid stream as well as its pressure depend, of course, upon the width of the desired cut and upon the hardness of the material to be treated. Preferably for the cutting and drilling of metallic bodies, the high-presure jet should emerge from an aperture of 2 to 3 mm. in diameter and should be relatively parallel, i.e. with a spray-cone angle of approximately zero. The pressure should approach the upper pressure limit given earlier while the particles may be of sand, quartz sand, corundum and like conventional abrasive particles. In this manner, it is possible to cut and drill hand aluminum alloys with low melting points, hardened metallic surfaces (e.g. of metal carbide), relatively hard and difficult-tomachine metals such as stainless steel rods and plates (e.g. V2A-steel). Under the circumstances indicated earlier, it is possible, in accordance with this invention, to penetrate steel plates of this latter steel composition to a depth of many centimeters.

According to a further feature of this invention, as indicated earlier, the present invention is also applicable to the material-removing treatment of a metallic surface by mechanical means. The process can be used in place of conventional grinding and polishing systems and it has been found that it is possible to confine the treatment to a limited area dependent solely upon the geometry of the nozzle. For a polishing of a metallic workpiece of substantially any hardness, without the formation of impact craters and the lodging of contaminants in the workpiece surface, we prefer to use a minimum liquid pressure of 100 atmospheres and a relatively wide spray. In this case, the aperture of the nozzle may range up to, say, 20-30 mm. in diameter. Such an arrangement contracts with the use of the system for cutting purposes in which the nozzle aperture may be reduced to one tenth while the pressure of the liquid may be increased ninefold. Moreover, the jet can be fan-like or of other configurations adapted to promote wide coverage. While best results are obtainable when the abrasive is mixed with the liquid in the nozzle, it is also possible to form the mixture at the surface of the solid by applying abrasive particles thereto or forming them in situ. This latter system involves the use of incompletely rigid concrete or other aggregatecontaining composition as the treated solid. When such body is treated with the liquid jet, the aggregate or other granular components of the composition are loosened and entrained by the liquid along the solid surface.

Still another aspect of this invention resides in the use of the system for the cooling or drilling of synthetic stone bodies (e.g. of concrete or other heterogeneous mineral mass as, for example, bound together by synthetic resins) or natural stone. In general, the conventional rock-breaking methods using pneumatic hammers and drills are difficult to use with concrete and other relatively hard stone bodies and result in considerable tool wear and time-consuming efforts. Furthermore, the hammering or drilling of the bodies often gives rise to flying chips, rock splinters and flakes which endanger the health and wellbeing of the workers. The conventional processes are also unsatisfactory for the drilling or cutting type of cutting pipe, especially when these bodies are relatively long, and one must resort to handwork with hammer and chisel for effective and accurate processes. A further disadvantage of conventional arrangements, when they require grindstones and the like is that these abrasive bodies must be composed of diamond particles or other relatively expensive substances. In accordance with this aspect of the invention, therefore, the process permits the cutting or drilling of natural stone bodies (e.g. in quarrying or sculpture) and of synthetic stone work (e.g. of concrete or aggregate-filled compositions) even of the hardest character without wear of tools, without generating chips or splinters and without the development of impact stresses or the line.

When dealing with mineral bodies (i.e. natural or synthetic stone work as described above) it has been found that the process whereby a granular or particulate mineral substance is entrained in a high-pressure, high-velocity liquid stream against the surface, acts in a manner of a grinding wheel or oil stone to erode the surfaces of the mineral body without the disadvantages of impact working thereof. Here, too, the entrainment of the particles in the liquid stream causes the diversion along the surface of the body so that the bodies act as individual grinder grains moving parallel to the workpiece but forced thereagainst by their original kinetic energy. Furthermore, the width of the out can easily be dimensioned by properly choosing the nozzle aperture and the depth of the cut per pass is proportional to the quantity of abrasive particles, the liquid pressure and the liquid velocity on impact. The particles used in this system include sand, quartz sand, corundum and the like while best results are obtainable with a nozzle aperture of up to 5 mm. but preferably 2-3 mm. (diameter) and a liquid pressure no less than atmospheres and preferably ranging up to 900 atmospheres.

When the present invention is used for the descaling of metal surfaces (e.g. weld seams, wires, plates, cast-iron bodies and the like), pressure within the range mentioned above but preferably up to only 550 atmopheres and particle sizes between 0.01-3 mm. (preferably 0.1 to 1 mm.) I

are employed.

According to still another aspect of this invention, the apparatus for treating solid surfaces with the high-velocity high-pressure jet of liquid-entrained abrasive particles includes an injector-type or venturi nozzle through which the high-pressure liquid is forced and into which the particle stream is induced. The apparatus thus includes a highpressure liquid pump connected via a high-pressure conduit with a nozzle having an injector-type or venturitype insert and to which a further conduit for the granular material is affixed. The high-pressure pump is preferably a multiple-piston pump of conventional construction provided with equalizing or leveling means (e.g. pressure-relief or bypass valves) to ensure a uniform output with a minimum of pulsation.

It has been found to be highly desirable and it is, accordingly, another feature of this invention that the nozzle body includes a connecting portion afiixed to the highpressure conduit, and a discharge portion forwardly of this rearward portion whose axis is inclined to the axis of the connecting or rearward portion at an obtuse angle. Thus the aperture axis and venturi insert may be inclined to the axis of the body at the connecting portion while the abrasive-supply conduit is likewise inclined toward the axis of the venturi insert forwardly in the direction of the aperture. In this manner, the nozzle is able to be inserted axially into a tube or the like such that the high-pressure jet is directed at the inner surface of the tube even though the high-pressure conduits extend axially therealong. When the system is used for the cutting of concrete pipe or the descaling of centrifugal cast metallic pipe, we prefer to mount the body to be treated upon at least a pair of rollers engaging its periphery and to set the body in rotary motion. The nozzle thus inserted into the tube likewise is provided with a pair of stabilizing rollers, engaging the inner periphery of the horizontal tube, whose axes are parallel to the tube axis and which support the nozzle while directing the jet against the scale Within the tube even while the tube is rotating. The rollers, of course, are provided along a side of the nozzle body opposite that at which the aperture opens. When the nozzle is not angular but is generally axial, we have found it advantageous to form the venturi insert as an axially projecting tube extending into a mixing chamber but terminating short of the aperture or outlet. The abrasive-supply tube then opens into this chamber between the end of the insert and the region at which it joins the wall of the nozzle body.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic elevational view of an assembly for the descaling of centrifugally-cast iron pipes, the descaling of welded seam pipes, the truing or polishing of internal surfaces of concrete pipes, or for the drilling of pipes of substantially any composition;

FIG. 2 is a cross-sectional view taken generally along the line IIII of FIG. 1;

FIG. 3 is an axial cross-sectional view through the pipe of FIG. 1 showing in operation the descaling heads for internal and external surface treatment of the solid body;

FIG. 4 is an axial cross-sectional view through a nozzle serving for the external-surface treatment of the body of FIG. 3 and suitable for drilling or cutting metal or mineral bodies as set forth aboveand/ or for the material removal treatment thereof;

FIG. 5 is a cross-sectional view through a modified nozzle assembly according to this invention; and

FIG. 6 is a detail view diagrammatically illustrating the principles of the present invention.

Referring first to FIG. 6, it will be seen that, by contrast with sandblasting or shotpeening systems for the surface treatment of a body B, the tream of liquid L (entraining solid abrasive particles diagrammatically illustrated at A) impinges upon the surface S of the body. Because of the viscosity and entrainment characteristics of the liquid, instead of the particles A rebounding from the surface S after pitting the latter, a film F of liquid flows over the surface in the region of impact and the particles are diverted at least in part at A and A" along this surface S. Thus the liquid and the original kinetic energy of the particles and the jet forces the particles against the surface with a wiping action so that the particles A and A' have a velocity component or a component of movement parallel to the surface (arrows V' and V) as well as a component C perpendicular to the surface. The resultants R and R" thus act to erode the surface S rather than pit it and the liquid washing at high pressure and velocity across the surface acts as a grinding stone urged with a similar resultant force thereagaint. It will be undertood, of course, that a portion of the particle-entraining liquid will-at the elevated pressures and velocities-be reflected from the surface as represented by arrow D and D". Furthermore, the viscosity of the liquid and the kinetic energy of the molecules of the latter limit rebounding of the particles from the surface while serving to lubricate the flow of particles away from the impact area so that the particles do not wedge into pores of the surface. Heating effects produced by the dissipation of kinetic energy in the form of heat are limited because of the effective heat exchange between the liquid film F and the surface S of the body B. Moreover, the high velocity of the liquid ensures a rapid carrying away of the evolved heat.

In FIGS. 1 and 2, we show a device for the simultaneous descaling of the inner and outer surfaces of centrifugally-cast iron pipe 1. This pipe 1 is produced by any conventional centrifugal casting process and is composed of cast iron upon which a scab or scale of highly adherent oxides and iron particles and/or particles derived from the mold. The pipe 1 is, as illustrated in FIGS. 1 and 2, mounted upon a pair of supports 2 each of which is formed with a yoke 2' carrying a pair of rollers journaled for rotation about axes parallel to that of the centrifugally cast pipe .1. The distance between the rollers of each pair is less than the outer diameter of the pipe 1 so that the pipe may rest on the rollers 3 which, in turn, frictional-ly engage the outer periphery of the pipe. The rollers 3 may be driven by a motor M of any conventional type so that the pipe can be rotated about its axis as represented by arrows 25. To descale, strip or clean the internal surface of the pipe 1, we provide an internal nozzle 4 (FIGS. 3 and 5) which projects a high-pressure water jet, entraining solid abrasive particles of sand, quartz, corundum or the like against the internal surface. While the major fraction of the jet is shown in FIG. 3 as it strips the scale 26 from the inner surface 27 of the pipe 1, it will be understood that, to a large measure, the heterogeneous jet flows as -a film over the surface with greater significance as an abrasive flow than as an impacting stream. The outer surface 28 of the pipe 1 is treated with a jet 7 of high-pressure, high-velocity water entraining similar particles. This jet 7 strips the scale 29 from the outer surface 28. The nozzle 6, producing jet 7, is best seen in FIG. 4.

As illustrated in this latter figure, the nozzle 6 comprises an outer nozzle housing 9 threaded at 30 onto a connecting body 12 provided with an axial bore 31. The connecting body 12 is formed with a threaded portion 32 by means of which a high-pressure hose 13 may be con nected to the nozzle 6 via a union-type nut coupling 33 (FIG. 3). An injector inserter 8 is threaded into the boss 34 of the connecting body 12 and has a central passage 35 axially aligned and registering with the bore 31. The constricted outlet 36 of the forwardly frustoconically tapering portion 37 of the tubular insert 8 opens into a mixing chamber 38 defined around the insert 8 and between the latter and the housing 9. The mixing chamber 38 converges, forwardly of the outlet 36, in the direction of an exchangeable nozzle tube '10 whose aperture 39 defines the width of the jet 7 and the spray-cone angle thereof.

For the purpose of interchangeability, the aperture member 10 is threaded at 40 into the mouth of housing 9. A connecting fitting 11 constitutes a tube welded at 41 to the housing 9 and opening into the chamber 38 rearwardly of the outlet 36. Tube 11 has an axis inclined forwardly to the axis 42 of the nozzle and has a threaded portion 43 to which a supply conduit 15 (FIG. 3) may be attached at a fitting 44. Thus a high-speed, high-pressure stream of liquid emerging from the outlet of 36 of the venturi tube 8 will produce a reduced pressure in the chamber 38 behind this outlet to draw particulate material from a supply hopper via pipe 15 into the mixing chamber for entrainment with the liquid stream ejecting through aperture member 10.

Referring now generally to FIG. 1, it will be seen that the high-pressure line 13 is connected with a pressure generator 14 capable of generating at hte nozzle 6 or the nozzle 4 a liquid pressure of between 100 and 900 atmospheres. The pressure generator 14 is a conventional multipiston liquid pump having pressure-equalizing and surge-reducing means of the character described. The pump 14 is also connected to a source of water such as a sump channel 20 via a return pipe 22. Any other source of water will also be suitable. The abrasive-supply conduit 15 is connected with a hopper or other supply means 16 containing loose sand. Thus, as a general matter, the sand is induced by the reduced pressure generated in pump 38 (in accordance with the venturi principle) to flow into the chamber 38 in which it is mixed with a high-velocity stream of water and carried thereby through the aperture number 10, the latter can easily be replaced if its interior surfaces are significantly eroded by the heterogeneous mixture passing therethrough.

Referring again to FIGS. 3 and 5, it will be seen that the inner surface 27 of pipe 1 is treated by the jet 5 which impinges thereon in a forwardly inclined direction from the nozzle 4. The latter comprises a connecting body 12 and a housing portion 9 welded thereto such that an obtuse angle is formed between the axis 42a of the connecting portion and the axis 42b of the housing portion 9'. The housing portion 9 defines a chamber 38 which at least partly surrounds a tubular venturi insert 8' interchangeably mounted in the housing 9 reaiwardly of the discharge end of the nozzle. This discharge end is formed with an aperture member 10' which is clamped by a nut .17 threaded onto the housing portions 9, against the mouth of the latter. The aperture member 10' is formed wtih a tubular portion 10a passing through the nut 17 and an integral disk portion 10b held by the nut 17 against the front-end surfaces 9a of the housing. The tubular vent insert 8 is provided with a forwardly converging and constricting outlet 36 while being held with its shoulder 8a against the housing 9 by a threaded clamping disk 8b screwed onto the thread 9b of the housing. The connecting portion 12 of nozzle 4 may be connected to the high-pressure pipe 13 via a nut assembly 33 in the manner previously described. Also in the manner described with reference to FIG. 4, a tubular fitting 11' is welded to the housing portion 9' and communicates wtih the mixing chamber 38' while being inclined forwardly to the axis 421) in the direction of the exchangeable aperture member 10'. Tube 11' may, in turn, be connected with an abrasive supply pipe 15'. Pipe 13, 13 (FIG. 1) and 15, 15 are connected in parallel to the pump 14 and the hopper 16, respectively. The interchangeable aperture members 10' can be replaced when worn by the stream passing therethrough and may also be interchanged to vary the diameter of the discharge aperture in accordance with the flow rate and jet configuration desired.

The angular orientation of the nozzle 4 of FIG. 5 obviously permits this nozzle to be insertedreadily into the pipe as illustrated in FIG. 3 without increasing or decreasing the impact angle of the jet in an uncontrolled manner. To position the jet 5 properly, we provide a pair of rollers (one shown at 18 in FIG. 3) upon the connecting portion 12' and journaled for rotation about axes parallel to that of the pipe 1. These transversely spaced rollers 18 support the nozzle 4 in the position shown as the pipe 1 rotates and the nozzle 4 is fed gradually into the tube in axial direction. As also shown in FIG. 1, the end of the outlet side of pipe 1 can open toward a shield 19 which deflects the efiluent detritus-carrying liquid 45 downwardly into the trough-like sump 20 and through a sieve conveyer 21 which can carry off the sand and other granular material for recovery if desired. The filtered liquid is connected at 22 and may be returned to the pump 14.

While the apparatus illustrated in FIGS. 1-5 has been described with reference to a descaling system for cast-iron pipe, it will be apparent that the nozzles 4 and 6 of FIGS. 4 and 5 can be used for the other cutting, drilling, descaling and surface-treatment processes described in the examples given below and that, in each case, the nozzle may be coupled with a multipiston pump 14 and an abrasiveparticle hopper 16. Similarly, a sump 20 and a deflecting plate 19 will also generally be provided.

EXAMPLE I Using the apparatus illustrated in FIG. 1 in which the centrifugally-cast pipe 1 was mounted generally horizontally but with a slight downward inclination toward the sump 20, the cast-iron pipe removed from the mold had an inner diameter of mm. and an outer diameter of mm. With nozzles as illustrated in FIG. 3, directing respective jets with a diameter of 5 mm. against the inner surfaces of the tube. The outlet apertures of the nozzles were of 5 mm. diameter. An initial test was carried out without an abrasive additive using only pure water at a pressure of 400 atmospheres. After a considerable treatment in this manner, the surface was examined and found to have been cleaned only of loosely adherent contaminants but to have considerable scale and scab. In a second test using quartz sand (quartz particles) with a particle size of 0.5 to 1 mm., as entrained by the same volume of liquid also at 400 atmospheres, it was found that a treatment for 20 seconds produced a metallically clean surface free from slag inclusions oxide scales and adherent metallic scab. Flaws in the metal were readily visible and both the interior and exterior surfaces were freed of all contaminants as well. It was found that a mere 5-second treatment was required to remove the slag layers.

EXAMPLE II Using the nozzle 6 of FIG. 4, a jet of ash-entraining water at 400 atmospheres was directed against a weld seam of a pair of steel plates. The abrasive here was fly ash obtained from dust-removal devices in an industrial furnace and having a particle size of the order of 0.1 to 1 mm. diameter. After 20 seconds of surface treatment, long-term rust was completely stripped from the plates and the scale of the weld seam fully removed so that chipping and wire brushing was not required. The weld seam appeared metallically clean and lightly abraded so that defects were readily discernible.

EXAMPLE III Using ordinary sand (particle size 0.5 to 1 mm.) entrained in a water stream at 400 atmospheres pressure and two nozzles 6 directed toward one another, a steel wire of 1 cm. diameter was drawn between the jets after having been coated with rust and scale by prolonged exposure to a moist atmosphere. The emerging wire was found to be free of grease, oxide scale and contaminants and to have a uniformly smooth shiny metallic appearance.

EXAMPLE IV Using the nozzle of FIG. 4, a jet of water-entrained corundum particles (of corundum with a particle size of 0.1 to 2 mm. diameter) was used to cut a concrete plate 5 cm. in thickness. The jet pressure was 900 atmospheres and the width of the jet at contact with the concrete plate was 2.5 mm. The jet penetrated in the concrete plate within an hour and was advanced linearly over more than a meter. The width of the slot formed in the plate was slightly greater than 2.5 mm. and the cut was uniform throughout its length. Under the same conditions, a polyester bounded composition containing stone aggregate was cut through in half the time for a corresponding thickness. The same nozzle, pressure and particles were used to drill the concrete plate and it was found that holes of about 3 cm. in diameter could be formed in a matter of minutes per hole merely by advancing the nozzle in the direction of the concrete slab. When the nozzle was moved rapidly over the concrete slab, grooves or channels were formed therein with well-defined and uniform walls. When ordinary sand, quartz particles and free ash were used as the abrasive particles, similar results were obtained although the cutting effect was somewhat slow.

EXAMPLE V Using a nozzle of the type illustrated in FIG. wherein the aperture member was interchanged to test the results obtained when apertures of 1.5 mm., 2 mm., 2.5 mm., 3 mm., 5 mm., 10 mm., mm. and 30 mm. were substituted in turn and each of the nozzles was tested with water pressures at the nozzle of 100 atm., 150 atm., 200 atm., 400 atm., 600 atm., 800 atm., and 900 atm., the following results were observed with respect to the polishing and grinding of workpiece surfaces. In each case, when only pure water was used, only a Washing effect was observed even at the highest pressures. Rough metallic surfaces were not smoothed and no grinding phenomenon was effected. When an air-entrained jet of sand (particle size about 2 mm. diameter) was swept across the metallic surface, a scouring was obtained with pressures up to about 300 atmospheres with nozzles up to 2.5 mm. diameter. Larger diameter nozzles and the higher pressures corresponding to the pressure stage mentioned above merely resulted in a cleaning of the surface. At the highest pressures pitting of the surface was encountered and many particles remained lodged in pores formed in the surface. When water entrainment of sand particles with a particle size of 0.1 to 0.5 mm. was used, it was found that even at pressures as low as 100 atmospheres, an abrasive polishing of the surface resulted and the surface had the appearance of being abraded with a grindstone or emery cloth. Nozzle apertures for all pressures of less than 2 mm. diameter were found to be of reduced effectiveness as were apertures of greater than 3 mm. when channeling was of interest. Pressures above 900 atmospheres resulted in a considerably increased wear of the aperture members and a decrease in the ability to control the surface treatment. Pressures below 100 atmospheres were ineffective. All that was required to polish the surface was a sweep of the nozzles therealong and the degree of erosion was found to be directly related to the volume of the heterogeneous mixture used.

EXAMPLE VI When the 5 mm. nozzle was "used with 400 atm. water pressure to treat the surface of an incompletely bonded concrete, it was observed that the sand and aggregate loosened by the jet acted as abrasive particles to smooth the surface in the manner described. As the surface was smoothed, there was less tendency for abrasive particles to be generated in situ and sand was thereafter deposited on the surface for final finishing.

The invention described and illustrated is believed to admit of many modifications Within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

We claim:

1. A method of treating the surface of a solid, comprising the steps of:

(a) mixing a particulate material from the group which consists of sand, quartz particles, corundum and fly ash with a particle size of 0.01 mm. up to 3 mm. with water to form a heterogeneous mixture;

(b) directing said mixture in a jet having a diameter of 2 to 3 mm. at high velocity and an elevated nozzle pressure of substantially to 900 atmospheres against said surface whereby said water carries particles of said material along said surface and in abrasive contct therewith; and

(c) recovering the mixture upon impingement against said surface and recirculating the recovered mixture to said jet.

2. The method defined in claim 1 wherein said body is a cast-iron pipe to be descaled and said mixture is directed against both the internal and external surfaces thereof from respective jets, further comprising the steps of rotating said pipe about its axis, axially advancing said jets relatively to said pipe while rotating same to sweep said jets along substantially the entire inner and outer surfaces of said pipe.

3. The method defined in claim 1 wherein said solid is a body to be subjected to mechanical material-removing treatment over a limited region of said surface and said jet is dimensioned to sweep only said limited region.

4. The method defined in claim 1 wherein said particulate material consists of particles having a particle size of about 0.1 to 1 mm.

References Cited UNITED STATES PATENTS 1,952,848 3/1934 Eckler 51-14 2,015,875 10/1935 Sloan 51-321 X 2,040,715 5/ 1936 Smith 51-321 2,092,083 9/ 1937 Ogle et al. 51-8 2,200,587 5/ 1940 Tirrel-l 51-321 X 2,380,738 7/1945 Eppler 51--321 X 2,489,097 11/194 9' Luce 51-321 2,951,319 9'/1960 Kornhaus 51-8 2,985,050 5/1961 Schwacha 51---321 X LESTER M. SWINGLE, Primary Examiner.

US. Cl. X.R. 

